The present invention relates most generally to polishing operations which use a polishing slurry, and more particularly to a method for removing microorganism contamination from a polishing slurry used in conjunction with a chemical mechanical polishing apparatus used for polishing in the semiconductor manufacturing industry.
Polishing operations which use polishing slurries find application in various technical fields. A commonly used polishing operation is a chemical mechanical polishing (CMP) operation used to polish substrates in the semiconductor manufacturing industry. CMP polishes a substrate surface by applying a force to mechanically urge the polishing surface against a rotating polishing pad, and also by providing a polishing slurry to the interface formed between the polishing pad and the surface being polished within the CMP apparatus. Slurries generally include both chemical and abrasive components. Slurries commonly used in the semiconductor manufacturing industry may include 20-30% solids and will include abrasives such as silica colloidal solids. The size of the abrasives may range from 50 nm-300 nm in diameter. Slurries also generally include chemical components. Generally speaking, slurries used for polishing metal films are acidic in nature, and slurries used for polishing oxide or other dielectric films are basic in nature. Slurries which are used for buffing, commonly used as a final step in the polishing operation, are generally neutral solutions having a pH within the range of 6 to 8.
Particularly in neutral pH slurries, microorganisms may be present, although some forms of microorganisms can survive and may be present in slurry solutions having a pH within the extreme basic or acidic range. Once present in a slurry solution, microorganisms can grow and multiply. Microorganisms tend to agglomerate and may chemically and physically contaminate the surface being polished, or the devices formed within the surface being polished. In their agglomerated state, microorganisms combine to form large particles, which can produce scratches and other defects on the surfaces of the semiconductor devices which are being polished. These scratches and other defects can destroy a very large number of integrated circuit devices being formed within the substrate. As the features of the integrated circuit devices being produced within the semiconductor substrates continue to shrink, the devices become increasingly more sensitive to scratches and other mechanically formed defects.
Slurry solutions having high concentrations of microorganism contamination, and especially those with agglomerated microorganism contaminants, also cause other problems such as clogging within the tubing and other components of the fluid delivery system used to deliver the slurry solution. As such, it is very desirable to remove microorganism contamination from polishing slurries.
One approach to removing microorganism contamination from slurries, is to add biocides to kill the microorganisms. However, this introduces another unknown species into the slurry which could degrade performance of the polishing operation. Biocides may include antibiotics and pesticides which contain chemicals which are harmful to the environment, harmful to the devices being polished, and which may be toxic to humans. As such, this approach is unsuitable for applications where the polishing operations are performed in close proximity to people who operate and service the polishing equipment. Furthermore, this approach is particularly unsuitable for operations such as the chemical mechanical polishing of semiconductor devices, where the devices being formed within the substrate being polished are very sensitive to foreign chemical species being introduced to the surface to be polished.
It can be seen that there is a need for a method for removing microorganism contamination from a polishing slurry without adding harmful additives to the slurry or otherwise adversely compromising the slurry integrity or quality or safety.